A heat exchanger which comprises an outer shell, a core disposed centrally in this shell or housing, means for admitting a fluid to the shell and drawing a fluid from the shell, and a tube bundle disposed around the core within the shell and traversed by one or more of the fluids, is commonly in use in low-temperature technology for the direct heat exchange of two or more fluids.
Of particular interest of late is a system of this type in which the tube bundle consists of a multiplicity of coaxial layers of heat-exchanger tubes, each layer comprising a multiplicity of helically coiled tubes, i.e. a plurality of coils. At the ends of these layers, the tubes can extend axially from the respective coils and pass through the housing or into a manifold within the housing whereby a fluid is fed to or withdrawn from the respective layers.
In order to hold the tubes of successive coaxial layers in the requisite spaced relationship to facilitate uniform passage of the surrounding fluid through the housing and between the tubes, spacers are generally employed. Furthermore, it is necessary to retain the tubes of at least the initial and terminal turns of each layer in a fixed relationship to one another, to the core tube and to the housing. This can also be accomplished by clamping members which have a comb-like configuration into the recesses, notches or cavities of which the tubes of the layer are placed and to which the tubes are welded to retain each tube in a fixed location with respect to the clamping member or spacer.
The distance between adjacent tubes within the layer and between layers is relatively small and frequently the tubes are extremely thin so that welding to regain the tubes in position poses problems of possible penetration of the tube wall, insufficient anchoring of the tube turn or the like. It will be understood that massive welds which would insure firm attachment of the tube coils are precluded by the nature of the tube while, on the other hand, an insufficient weld attachment will render the spacers, clamping members and the like, ineffective.
Should the tube wall burn through, it is necessary to either remove the entire coil or seal off the coil (i.e. forming a blind coil) which removes the same from participation in the heat exchange operation.
Among other disadvantages of inadequate welds is the tendency for the turns or coils to develop nonuniform diameters and thus interfere with the insertion of the tube bundle in the heat exchanger's shell or housing, removal of the tube bundle therefrom in the event repair is necessary, etc.
Thus the art has long been confronted by the problem of fixing, at least at the terminal turns, multilayer helically-coiled heat-exchanger tubes with respect to one another, i.e. between layers and between turns of a layer, retaining these tubes in precise positions without welding, and maintaining uniform cylindrical configurations of the various layers of the tube bundle. A successful solution to the problem offers simplification in the construction of such heat exchangers, increased efficiency by reducing the number of turns or coils which may remain in the unit but are ineffective, and reduced labor expenditure in constructing such heat exchangers.